Although ash from Iceland’s Grímsvötn Volcano initially remained localized, by May 24, 2011, the ash cloud had spread over the North Sea. This pair of natural-color satellite image shows a dense plume of ash between Scotland and Norway (top), and ash spreading from Iceland across the North Atlantic (lower). The London Volcanic Ash Advisory Center (VAAC) reported the ash at an altitude of 20,000 feet (6,100 meters) at 12:00 UTC, 50 minutes after the top image was acquired. According to EUROCONTROL, The European Organisation for the Safety of Air Navigation, approximately 250 flights were cancelled in the United Kingdom due to the ash, and flights in southern Scandinavia were likely to be cancelled as well.

The top image was acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra satellite at 11:10 UTC. The lower image was acquired several hours later, at 13:05 UTC, by the MODIS instrument aboard Aqua. In both images, the tan volcanic ash plume is visible beneath moderate cloud cover.